Ring core meter movement

ABSTRACT

An electrical current responsive movement for ring core moving coil meters and the like wherein the magnet and its pole pieces have mating interfitting formations, such as tongue and groove formations, which join the pole pieces to the magnet without the aid of solder, adhesive, or other fastening means.

United States Patent Inventor Edwin L. Schwartz Los Angeles, Calif. App]. No. 812,197 Filed Apr. 1, 1969 Patented July 13, I971 Assignee Rite Autotronies Corporation Los Angeles, Calif.

RING CORE METER MOVEMENT 5 Claims, 8 Drawing Figs.

11.8. CI. 324/151 A, 29/607, 335/302 Int. Cl 6011 1/16 Fieidolseareh 324/151, 151 A; 335/302; 310/216; 336/216, 210; 29/203, 205, 602, 607

[56] References Cited UNITED STATES PATENTS 2,792,511 5/1957 Horstman..................... 310/216 2,808,567 10/1957 Lederer 324/151 (A) 2,978,640 4/1961 Arbeiter et a1 324/151 (A) Primary Examiner-Alfred E. Smith Attorney-Robert E. Geauque ABSTRACT: An electrical current responsive movement for ring core moving coil meters and the like wherein the magnet and its pole pieces have mating intertitting formations, such as tongue and groove fonnations, which join the pole pieces to the magnet without the aid of solder, adhesive, or other fastening means.

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B Y R I ,4 rro/qvvi Y PATENTED JUU 3 I971 SHEET 2 OF 2 RING CORE METER MOVEMENT BACKGROUND OF THE INVENTION I. Field ofthe Invention This invention relates generally to the field of electrical current responsive devices and more particularly to an improved magnetic core assembly for a ring core current responsive movement.

2. Prior Art As will appear from the ensuing description, the invention may be utilized to advantage in a variety of electrical current responsive devices. However, the invention is concerned primarily with and will be disclosed in relation to electrical current responsive instruments, particular ring core moving coil meters.

Ring core moving coil meters an: well known in the art and are widely used as tachometers, voltmeters, anmeters, and so forth. A meter of this type has a current responsive movement characterized by a magnetic structure including an inner magnetic core assembly and an outer magnetically permeable pole ring. The ring and core assembly define an intervening annular airgap in which exists a magnetic fiux created by a magnet in the core assembly. Surrounding the inner core assembly, in a plane containing the axis of the airgap, is an armature coil which passes through the airgap. This coil is rotatably supported to turn on the axis of the airgap. When the coil is energized by connection of its leads to an external current source, a torque is produced on the armature by the interaction of its electromagnetic field with the magnetic field within the airgap.

The existing ring core meter movements of this type possess certain deficiencies which the present invention seeks to overcome. These deficiencies reside in the construction of the inner magnetic core assembly of these meter movements, Thus, in the existing meter movements, the inner magnetic core assembly is composed of a magnet and a surrounding magnetically permeable inner pole ring. This inner pole ring has a central opening in which the magnet is fixed by an interference fit, or by staking, soldering, or cementing the magnet to the ring. At its diametrically opposite sides, the inner pole ring is relieved or notched to effectively divide the ring into two diametrically opposite, generally sector shaped pole pieces. These pole pieces are joined at the ring notches by relatively thin reduced sections of the pole ring.

As noted above, this inner magnetic core assembly is surrounded by an outer pole ring. The outer pole ring is concentric with the pole pieces to define therebetween the annular airgap through which the rotary armature coil passes. The pole pieces provided by the inner pole ring are intended to distribute more evenly the magnetic flux within the annular airgap and thereby provide the meter movement with a more linear current response. It will be recognized, of course, that a linear current response is beneficial in an indicating meter because it permits the use of a readily reproducible readout scale with uniform scale divisions over its entire range.

While the existing ring core meter movements described above do achieve some degree of uniform magnetic flux distribution within the annular airgap, they suffer from the disadvantage that the reduced connecting sections of the inner pole ring which join the magnetic pole pieces permit flux leakage which distorts the airgap flux distribution, particularly in the vicinity of these connecting sections. This distorting produces nonlinear current response of the meter movements and creates the need for a nonlinear readout scale which may be difficult and costly to mass produce. Elimination of such distortion would require complete separation of the pole pieces. This, in turn, would necessitate elimination of the reduced connecting sections of the inner pole ring and attachment of the resulting separate pole pieces to the magnet by solder, adhesive, or other fastening means. However, the additional costs involved in soldering or cementing the pole pieces to the magnet is prohibitive. As a consequence, the existing ring core meter movements utilize the less desirable but more economical continuous inner pole ring configuration.

SUMMARY OF THE INVEN'I ION The present invention provides an improved inner magnetic core structure or assembly for a ring ct re electrical current responsive movement of the class described. This ring core movement possesses the advantages of a relatively uniform magnetic flux distribution within the annular airgap which yields a relatively linear current response, and reduced cost of manufacture. To this end, the inner magnetic core structure is characterized by a magnetic assembly including a pair of spaced, separately formed magnetically permeable pole pieces, a magnet between the pole pieces, and mating inter fitting formations on the pole pieces and magnet which join the pole pieces to the magnet without the aid of solder, cement, or other fastening means. These interfitting formations are shaped to permit assembly of the magnet and pole pieces by simply sliding or snapping the parts together, in effect. In the disclosed embodiment of the invention, for example, the pole pieces and magnet are joined by interfitting tongue and groove formations. The inner parts or tongues of these formations are dimensioned to have an interference fit within the outer grooved parts, such that the parts are retained in assembled relation by the interference fit.

As noted earlier, the improved magnetic core structure or assembly of the invention may iseJ in a variety of ring core current responsive movements. The particular embodiment of the invention illustrated is a ring core meter movement of the type utilized in an indicating meter, such as a tachometer, voltmeter, arnmeter, or the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a front elevation of an electrical indicating meter embodying an improved ring core movement according to the invention;

FIG. 2 is an enlarged side elevation of the improved ring core movement embodied in the meter of FIG. I;

FIG. 3 is a section taken on line 33 in FIG. 2;

FIG. 4 illustrates the magnetic core structure of a conven tional prior art ring core meter movement;

FIG. 5 is an enlarged section taken on line 55 in FIG. 2;

FIG. 6 is a section taken on line 6-6 in FIG. 5;

FIG. 7 is a section taken on line 7-7 in FIG. 5; and

FIG, 8 illustrates the magnet and a pole piece of the present improved ring core structure.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to these drawings, there is illustrated an improved ring core current responsive movement 10 according to the invention. In this case, the movement is embodied in an indicating meter 12 which may be a tachometer, voltmeter, ammeter, or the like. The ring core movement I0 has an inner magnetic core structure or assembly 14 which is uniquely constructed in accordance with the invention and a surrounding outer magnetically permeable pole ring I6. The outer pole ring and the inner core assembly are concentrically disposed to define therebetween an intervening annular airgap l8. Surrounding the inner core assembly 14 in a plane containing the axis a of this airgap is an armature winding 20. This armature winding passes through diametrically opposed portions of the airgap and is rotatably supported to turn on the inner gap axis The inner magnetic core structure or assembly 14, which represents the major contribution of the present invention, has a pair of totally separate magnetically permeable pole pieces 22, an intervening magnet 14, and mating interfitting formations 26 on the pole pieces and magnet for joining the same without the aid of solder, cement, or other additional fastening means. At this point, reference is made to FIG. 4 which illustrates the inner magnetic core structure of a conventional prior art ring core meter movement. In this case, the pole pieces P are part of an inner pole ring R which is notched at N to define the pole pieces. Within the central opening in the pole ring is a magnet M which is staked, cemented, press fitted, or otherwise secured within the ring. As noted earlier, the major disadvantage of this core construction is airgap flux distortion and resultant nonlinear current response. To eliminate such distortion would require complete separation of the pole pieces P and soldering or cementing of the separate pole pieces to the magnet M. This method of attachment of the pole pieces to the magnet, however, is too costly for a commercial meter movement so that the less desirable but more economical core configuration of FIG. 4 is generally employed.

The present improved core construction l4 substantially reduces airgap flux distortion without increasing cost and is thus vastly superior to the existing core construction shown in FIG. 4. Referring in greater detail to the drawings, the magnet 24 of the present core assembly 14 has a generally H shape and includes a pair of parallel cross members 28 and a connecting member 30 extending between and joining the cross members. These cross and connecting members define intervening corners containing 45 fillets 32. As will appear presently, these fillets constitute an important part of the invention as it is constructed in the disclosed embodiment. It will be observed that each cross member 28 and the adjacent end of the connecting member 30 of the magnet provides an essentially T'shaped formation on tongue 34. The pole pieces 22 have a generally semicircular or sector shape and contain generally T-shape slots or grooves 36 which receive, with an interference fit, the T-formations 34 on the magnet 24. This interference fit of the T-formations in the pole piece slots retains the magnet and pole pieces in assembled relation without the aid of solder, cement, or other fastening means. It will be immediately evident to those versed in the art that the T-formations 34 and slots 36 constitute the mating interfitting formations 26 referred to earlier. These mating formations obviously comprise essentially tongue and groove formations.

The interference fit of the magnet T-formations or tongues 34 in the pole piece slots or grooves 36 may be achieved in various ways. in the particular embodiment of the invention illustrated, the walls of the pole piece slot portions 38, 40 intersect to define edges 42 that bite into the magnet fillets 32 to provide the interference fit.

When the pole pieces 22 and magnet 24 are assembled, the outer curved edges of the pole pieces are centered on a common axis which is the rotation axis a of the armature 20. The inner confronting edges of the pole pieces are spaced to define therebetween high reluctance airgaps 44 which substantially reduces, if not virtually eliminates, magnetic flux leakage between the pole pieces. As noted earlier, the outer pole ring [6 concentrically surrounds the inner core assembly 14 to define therebetween the annular airgap IS. The inner core assembly and outer pole ring are joined by means 46. In this case, the means 46 comprise a pair of generally U-shaped brackets 48 located at opposite sides of the core assembly and outer pole ring. These brackets have ends 50 which project into the pole piece airgaps 44 and are notched at 52 to receive the pole pieces, as shown. The two brackets are clamped to the inner core assembly 14 and the outer pole ring l6 by bolts 54 which pass through flanges 56 on the brackets to secure these parts in rigid assembled relation.

In the disclosed embodiment of the invention, the brackets 48 serve the additional function of bearing supports for the armature 20. Thus, the annature has a shaft 58 journaled at its ends in jewel bearings 60 carried by the brackets 48. These jewel bearings are made adjustable in the usual way. The ends of the armature coil wire are attached to springs 62 which bias the armature to a neutral position. Leads 64 extend from the outer ends of these springs for connection to an external current source.

It is now evident that the present'current responsive movement operates in the usual way. Thus, when the armature coil is energized through its leads 64, the electromagnetic field about the coil interacts with the magnetic field in the airgap [8 to produce a torque in one direction on the armature. This torque rotates the armature against the action of its springs 62 to locate the armature in an angular position re lated to the current flow through the armature coil. Because the pole pieces 22 of the inner core assembly 14 are totally separated by the intervening airgaps 44, the magnetic flux distribution within the airgap 1B is quite uniform. As a result, the present ring core movement 10 has a relatively linear current response. The particular meter [2 in which the movement is embodied has a needle 66 which is attached to the armature shaft 58 and rotates along and in front of a dial plate 68 when the armature turns. The needle and dial thus provide a readout related to the current flow through the armature coil.

While the invention has been disclosed in what is presently conceived to be its most practical and preferred embodiment, various modifications of the invention are obviously possible within the spirit and scope of the following claims.

What I claim as new in support of Letters Patent is:

I. A magnetic core assembly for a ring core movement of the class described comprising:

a pair of spaced magnetically permeable pole pieces;

a magnet between said pole pieces;

said pole pieces and magnet being shaped to provide mating interfitting formations which join said pole pieces to said magnet without the aid of other fastening means, said mating formations comprise tongue and groove formations,

the tongues of said mating formations have an interference fit within their respective receiving grooves to retain said pole pieces and magnet in assembled relation.

2. A magnetic core assembly for a ring core movement of the class described comprising:

a pair of spaced magnetically permeable pole pieces;

a magnet between said pole pieces;

said pole pieces and magnet being shaped to provide mating interfitting formations which join said pole pieces to said magnet without the aid of other fastening means;

said magnet has a generally H shape and includes a pair of spaced parallel cross members and a center connecting member extending between and joining said cross mem bers, whereby each cross member and the adjacent end of said connecting member defines a generally T-shaped for mation,

each said pole piece has a generally T-shaped slot receiving a T-formation of said magnet, and

said mating interfitting formations comprising said T-forma tions and slots.

3. A magnetic core assembly according to claim 4 wherein:

said T-formations are dimensioned to fit within said T-slots with an interference fit, such that said magnet and pole pieces are retained in assembled relation without the aid of other fastening means.

4. A magnetic core assembly according to claim 4 wherein:

each said T-slot has a first slot portion receiving a cross member of said magnet and a second slot portion opening through an edge of the respective pole piece and receiving the adjacent end of the connecting member of said magnet,

said slot portions of each pole piece have walls which intersect to define relatively sharp edges on the respective pole piece,

said cross members and said connecting member of said magnet have thicknesses less than the width of said first and second slot portions, respectively, and define interior comers each containing a fillet, and

said intersection edges of said pole pieces engage said fillets to provide said interference fit.

5. A ring core movement for electrical meters and the like comprising:

an inner magnetic structure including a pair of spaced generally sector shaped magnetically permeable pole pieces, a magnet between said pole pieces, said pole pieces and magnet being shaped to provide mating interfitting formations which join said pole pieces to said magnet without the aid of other fastening means, and said pole pieces having outer arcuate edges which are circularly curved about an axis passing through the approximate geometric center of said magnet,

a magnetically permeable outer pole ring surrounding said structure in concentric relation to said axis,

said ring and pole pieces defining therebetween an intervening annular airgap,

meansjoining said ring and structure,

an armature coil surrounding said structure in a plane containing said axis,

means supporting said coil for rotation on said axis,

said magnet has a generally H shape and includes a pair of spaced parallel cross members and a center connecting member extending between and joining said cross members, whereby each said cross member and the adjacent end of said connecting member defines a T-formation,

each said pole piece has a generally T-shaped slot receiving a T-formation of said magnet,

said mating interfitting formations comprise said T-forma tions and slots,

said means joining said ring core and inner core structure comprise a pair of generally U-shaped bearing supports at opposite sides of said structure and outer pole ring, said brackets having ends projecting between and seating the confronting edges of said pole pieces, and means clamping said brackets to said outer pole ring and said inner core structure to retain the same in rigid assembled relation, and

bearing means carried by said brackets and supporting said armature for rotation on said axis. 

1. A magnetic core assembly for a ring core movement of the class described comprising: a pair of spaced magnetically permeable pole pieces; a magnet between said pole pieces; said pole pieces and magnet being shaped to provide mating interfitting formations which join said pole pieces to said magnet without the aid of other fastening means, said mating formations comprise tongue and groove formations, the tongues of said mating formations have an interference fit within their respective receiving grooves to retain said pole pieces and magnet in assembled relation.
 2. A magnetic core assembly for a ring core movement of the class described comprising: a pair of spaced magnetically permeable pole pieces; a magnet between said pole pieces; said pole pieces and magnet being shaped to provide mating interfitting formations which join said pole pieces to said magnet without the aid of other fastening means; said magnet has a generally H shape and includes a pair of spaced parallel cross members and a center connecting member extending between and joining said cross members, whereby each cross member and the adjacent end of said connecting member defines a generally T-shaped formation, each said pole piece has a generally T-shaped slot receiving a T-formation of said magnet, and said mating interfitting formations comprising said T-formations and slots.
 3. A magnetic core assembly according to claim 4 wherein: said T-formations are dimensioned to fit within said T-slots with an interference fit, such that said magnet and pole pieces are retained in assembled relation without the aid of other fastening means.
 4. A magnetic core assembly according to claim 4 wherein: each said T-slot has a first slot portion receiving a cross member of said magnet and a second slot portion opening through an edge of the respective pole piece and receiving the adjacent end of the connecting member of said magnet, said slot portions of each pole piece have walls which intersect to define relatively sharp edges on the respective pole piece, said cross members and said connecting member of said magnet have thicknesses less than the width of said first and second slot portions, respectively, and define interior corners each containing a fillet, and said intersection edges of said pole pieces engage said fillets to provide said interference fit.
 5. A ring core movement for electrical meters and the like comprising: an inner magnetic structure including a pair of spaced generally sector shaped magnetically permeable pole pieces, a magnet between said pole pieces, said pole pieces and magnet being shaped to provide mating interfitting formations which join said pole pieces to said magnet without the aid of other fastening means, and said pole pieces having outer arcuate edges which are circularly curved about an axis passing through the approximate geometric center of said magnet, a magnetically permeable outer pole ring surrounding said structure in concentric relation to said axis, said ring and pole pieces defining therebetween an intervening annular airgap, means joining said ring and structure, an armature coil surrounding said structure in a plane containing said axis, means supporting said coil for rotation on said axis, said magnet has a generally H shape and includes a pair of spaced parallel cross members and a center connecting member extending between and joining said cross members, whereby each said cross member and the adjacent end of said connecting member defines a T-formation, each said pole piece has a generally T-shaped slot receiving a T-formation of said magnet, said mating interfitting formations comprise said T-formations and slots, said means joining said ring core and inner core structure comprise a pair of generally U-shaped bearing supports at opposite sides of said structure and outer pole ring, said brackets having ends projecting between and seating the confronting edges of said pole pieces, and means clamping said brackets to said outer pole ring and said inner core structure to retain the same in rigid assembled relation, and bearing means carried by said brackets and supporting said armature for rotation on said axis. 